Many solid state relay circuits are commercially available and a great many more circuits have been disclosed in the patent literature and elsewhere. Typically, these circuits operate in response to an input control signal of low magnitude to cause some bidirectional conduction device such as a triac to conduct to close a circuit that is connectable to a load and a higher a.c. voltage source. To minimize the creation of transients during switching of the solid state circuits it is common to include what has become known as zero crossover detectors to allow the triacs to be turned on only when the higher a.c. voltage source is at a very low magnitude near zero.
The present invention is an improved solid state relay circuit having the zero crossover switching feature. The circuit is less complex than some prior art circuits and provides improved reliability.